Control system for strip mills and the like



Jan. 5, 1937.

G. E. ADAMS ET AL 7 2,066,872

CONTROL SYSTEM FOR STRIP MILLS AND THE LIKE 4 Sheets-Shet 1 Filed Oct. 9, 1934' WIT/V556 I Jan. 5, 1937. G; E. ADAMS ET AL CONTROL SYSTEM FOR STRIP'MILLS AND THE LIKE 4 Sheets-Sheet 2 Filed Oct. 9, 1934 Gilber/ffiffldanza, dward G ilfansba WIT/V563 4 She'ts-Sheet s G. E. ADAMS ET AL Filed Oct. 9, 1934 CONTROL SYSTEM FOR STRIP MILLS AND THE LIKE Jan. 5, 1937.

TTORNEX w TNESS Jan. 5, 1937. E ADAMS ET AL v CONTROL SYSTEM FOR STRIP MILLS AND THE LIKE Filed Oct. 9, 1954 4 Sheets-Sheet 4 Patented Jan. 5, 1937 PATENT OFFICE CONTROL SYSTEM FOR s'rarr MILLS AND THE LIKE Gilbert Edward Adams Marshall,

Application October 9,

23 Claims.

Broadly considered, our invention contemplates the provision of an electrical control system, particularly for a plurality of electric motors arranged to work in conjunction with each other,

which is automatically operative to bring about controlled deceleration of the motors during that period in their operation at which deceleration is required, as determined by the number of revolutions yet to be made, in order to eifect their final stoppage at a predetermined point, and to effect such stoppage at that point. The system is therefore applicable to various industrial installations but is particularlyadapted for controlling the operation of tension rolling strip 25 the action of the motors and the parts driven' thereby, the current for the motors being supplied from any suitable source such, for example, as a motor-generator set. In the operation of a mill of this character, a usual practice is to first clamp 30 to one reel one end of the strip to be rolled and to then wind the strip upon it; the other end of the strip is then led through the reducing rolls and clamped to the opposite and now empty reel, following which both reels and the rolls are set in motion so the strip will be unwound from the first reel and, after its passage through the rolls,

wound upon the other until substantially the entire length of the strip has been acted upon. Thereupon, the mill is stopped and the direction of rotation of the parts reversed so as to pass the strip through the rolls in the opposite direction, these periodic reversals of the direction of travel of the strip being kept up until the desired reduction of the strip has been eifected, the size of the pass between the rolls being of course suitably diminished after each passage of the strip therethrough and the strip beingcustomarily maintained in tension between the unwinding reel and the rolls and between the latter and the winding reel, to which end the reel driving motors are generally so arranged and connected that each can be made to drive its respective reel or the latter can bemade to drive the motor and thus be prevented from too rapid rotation by the mills intended for progressively reducing the regenerative braking effect of the motor acting as and Edward Cru tchflcld Gary, Ind.

1934, Serial No. 747,494

a generator to exert the requisite tension on the strip.

Under practical operating conditions, effective control of a mill of this character has been a diflicult matter because of various factors neces 5 sarily entering thereinto, among which may be mentioned the following: It is of course desirable to move the strip through the rolls as rapidly and uniformly as possible commensurate with a proper rolling thereof so as to complete the desired re- 10 duction of the strip in the shortest practicable time with corresponding enhancement of the. productive capacity of the mill, but as it is visu-w ally impossible to accurately determine the num ber of turns oi strip upon the reels, especially when the latter are in motion and particularly at relatively high speeds, it is necessary for the operator to slow down and/or stop the mill intermittently each time the end of the strip is approached so as to avoid pulling the strip entirely oif the reel from which it is being unwound as can, of course, readily occur if the mill is in motion when the last turn is reached. This intermittent starting and stopping or slowing of the mill results in a distinct loss of. time and frequently in decrease of uniformity in the product while, moreover, it is not always efiective to enable the operator to determine the maximum amount oi the strip which may be unwound without danger of pulling it from the reel. Furthermore, the normal speed of travel of the strip through the mill varies widelyin accordance with the extent of reduction which has been efiected, it being customary to move the strip relatively slowly during the initial. pass or passes and to increase the speed progressively for each succeeding pass so that in the last pass the normal speed of travel may be as high as 1200 feet a minute while during the initial one it may be hardly more than a creeping speed, but at these higher speeds the control of the mill becomes increasingly diflicult due to the greater momentum of the parts, the thinner gage of the strip and the greater number of turns on the reels as the strip pro-. gressively elongates with each pass.

The control system of our invention when applied to a strip mill of the general character to which we have referred greatly minimizes or entirely removes these and. other difliculties of operation since it is automatically effective to produce a controlled deceleration of the roll and both reel motors after all but a predetermined number of turns of the strip have been drawn from the reel from which the strip is being unwound and, finally, to bring both said motors to rest when but one turn or thereabouts remains on the said reel, irrespective of the speed at which the strip is traveling through the mill or the number of turns of the strip on either or both reels. In consequence, the operator of the mill is relieved from the necessity of endeavoring to determine the proper time and point at which to begin deceleration of the mill and finally to bring it to rest while, on the other hand, he can tors arranged for conjoint operation in such manner that deceleration thereof will be automatically initiated at the proper time, as determined by the rolling speed to bring the motors to rest at the point at which stoppage is desired.

A further object of the invention is the provision, in conjunction with a strip rolling or generally similar mill comprising a pair of motor driven reels and a stand of motor driven rolls, of a control system which may be operated to automatically initiate a controlled deceleration of both reels and the main rolls when a predetermined number of turns remaining on the unwinding reel has been reached in the process of passing the strip being rolled from one reel to the other and through the rolls located therebetween, and to bring the rolls, reels and their respective motors to rest and terminate the period of deceleration after all, or all but one or fraction'of one, or. other desired number of turns have been unwound from the said reel.

A further object of the invention is to provide a novel form of fluid governor effective when utilized in a control system such as that of our invention to regulate the rate of deceleration after it has been initiated.

Other objects advantages and novel features of design, construction and arrangement of parts comprehended by the invention are hereafter more particularly pointed out or will be apparent to those skilled in the art from the following description of one embodiment thereof in operative association and combination with a strip mill of well known character as illustrated, in

large part diagrammatically, in the accompanying drawings in which:

Fig. 1 is a top plan view of a typical tension mill showing its actuating motors but omitting the several parts and connections relating to their control;

Fig. 2 is a vertical section thereof on the line 2-2 in Fig. 1;

Fig. 3 is a simplified wiring diagram showing the circuits employed in accordance with our invention for operating the control mechanism to effect automatic deceleration and stopme of the mill driving motors;

Fig. 4 is a fragmentary top plan view partly in section in the line 4-4 in Fig. 5 showing certain of the mechanical elements utilized in said control circuits, including the centrifugal fluid governor switch of our invention to which reference has been made;

Fig. 5 is a vertical section thereof on the line 5-5 in Fig. 4;

Fig. 6 is an enlarged fragmentary vertical section on the line 6-8 in Fig. 4 of the centrifugal fluid governor control switch and associated parts.

Fig. 7 is a simplified wiring diagram of typical energizing circuits which may be employed in a mill of the character shown in Figs. 1 and 2, with which the circuits shown in Fig. 3 may be interconnected for effecting controlled deceleration of the mill, and

Fig. 8is a graphic representation of a part of the cycle of operation of the mill Just prior to and during the deceleration period.

In the several figures, like characters are used to designate the same parts.

The typical tensionmill shown in Fig. 1 comprises a four-high roll stand I in which are rotatably disposed working rolls 2 provided with backing-up rolls 3, the working rollsbeing driven through a reduction gear from a direct current motor A. On opposite sides of the roll stand are disposed idler rolls 6L, 6R rotatably supported on suitable stands IL, IR to maintain a strip S substantially horizontal during its passage be-v tween the rolls 1, while at the opposite ends of the mill, outwardly spaced from the idler rolls, are disposed strip reels IIL, IIR respectively supported for rotation in stands IIL,- I IR. and provided with means (not shown) for clamping an. end of the strip 3 to their outer cylindrical surfaces. A drive shaft I2L for the left hand reel IL is interconnectedthrough gears ISL with the shaft ML of a direct current driving motor LRM and the transmitting motor STIL of a selsyn set, the purposes of which will hereafter appear, is driven through a flexible coupling ISL from the other end of this shaft. Similarly, the drive shaft IIR of the right hand reel IUR is interconnected through reducinggears IIR with shaft R of a direct current driving motor RRM to which in turn is connected, through a flexible coupling IBR, the transmitting motor STIR of another selsyn set.

In the normal operation of a mill of this character at the initiation of a rolling operation, one end of the strip 8 is clamped to the reel L and the motor LRM is actuated to drive this reel in a clockwise direction as viewed in Fig. 2, to wind the entire strip S thereon. The other end of the strip is then led over the idler 6L, between the working rolls 2, thence over the other idler OR and secured to reel IIIR. as indicated in Fig. 2. The strip being now in position for actual rolling, the rolls 2 are adjusted in the usual way, their driving motor A is energized to roll the strip in the direction of the arrow in Fig. 2, and the motor RRM energized to drive the reel IIR in acounterclockwise direction and thus wind the strip thereon after its passage between the rolls"2. Meanwhile, the circuit connected with motor LEM, geared to reel IIL from which the strip is now being unwound, is suitably controlled to provide a regenerative braking effect in the usual way to exert a desired tension on the strip and prevent too rapid rotation of reel "IL in a counterclockwise direction as the strip is drawn therefrom. As reel motors LRM and RRM rotate during this operation, the'selsyn transmitters STIL and STIR respectively rotate in unison therewith and their effect will hereinafter be more fully explained.

After substantially the entire strip has passed between the rolls 2 and been wound onto reel "R, the operation of the mill is arrested, preferably Just before its end Ls drawn from the unwinding reel ML, and the mill is then reversed and the strip passed in the opposite direction, being rewound. onreel' IL and unwound from reel I OR, the rolling being thus continued the requisite number of times to effect the desired.

reduction of the strip.

cal relationships and arrangements which are.

of course, in practice subject to modification; in Figs. 4-6 we have shown a convenient mechanical arrangement of certain of these elements, among which electrical connections are preferably extended as indicated in Fig. 3 and in Fig. 7 the mill motor energizing circuits to which the said control system is interconnected by leads, designated by the same symbols and included in the control circuits of Fig. 3.

Referring first toFig. 7, a motor DM, conveniently a constant speed alternating current motor, drives a generator G for supplying current to motors A, LRM and RRM through the leads a, b, across which the several motors are connected, the passage of this current being; controlled by an electrically actuated contactor C in a manner which will hereinafter appear. The fields of motors A, LRM and RRM are excited from any suitable source (not shown) by connection to power leads H5, H8, and those of motors LRM and RRM may be controlled through suitable rheostats practice to maintain the desired tension on the strip and for other purposes. The same current source is desirably employed for exciting the field 1 GI of generator G, and a reversing switch E controlled in accordance with customary practice by suitable variation of the generator field excitation, for which purpose there may be provided a variable rheostat H, operated by a re-' versible motor FM preferably of the series wound split-field type, and in the lead to one of these fields a switch J is disposed to permit manual control of the current flow therethrough to drive the motor in the proper direction to increase the generator field excitation to accelerate the mill, while in the lead to the other field is a similar switch K to drive the motor in the opposite direction to decrease the generator field excitation and hence decelerate the mill, the switches J and K being normally open except when positively actuated to close the circuits they respectively control. However, the operation of the field rheostat motor FM is subject to modification through the interconnection of our control system in its circuit as will be hereinafter more fully explained.

Referring now more particularly to Fig. 3

the selsyn transmitter STIL driven by left reel motor LRM as shown, is interconnected with a selsyn receiver SRIL in such way as to drive the in accordance with usual.

latter at the same speed as the former, motive power being derived from the leads I00, IOI, I02 interconnected through a main switch 20 to a suitable source of electric power, for illustration. 440-volt 3-phase A. 0. power supply LI, L2, L3, the rotors of these motors being interconnected through the leads I03, I04, I05 to effect synchronous rotation of the rotor of the receiver 'SRIL in correspondence with the rotation of that of transmitter STIL as the strip is' wound on left hand reel IOL. The selsyn receiver SRIL drives a shaft 25L to which is coupled a shunt-wound resetting motor RSL the purposes of which willv hereafter appear, and a selsyn transmitter ST2L. The latter derives its power from a transformer 26 through leads I06, I01, the primary coil of the transformer being supplied with 440. volt current from leads L2, L3, and is interconnected in synchronous driving relation with a selsyn receiver SRZL through power leads I06, I01 and rotor leads I08, I09, H0. .The receiver SR2L is positioned at the right hand control desk RD. and drives, through a flexible coupling 30R, a revolution counter 3 IR for giving a visual indicationof the number of turns made by left reel motor LRM in winding the strip on left reel IOL.

The shaft 25L also drives the mechanism for actuating the switches which effect automatic deceleration and stoppage of the mill motors when the end of the strip is reached. Said switches, as shown, include a mercury switch MIL actuated by a cam 35L mounted on a shaft 36L and driven through reducing gears 31L from shaft 25L, a similar switch M2L actuated by a.

of any desired type, suitable for cam actuation,

and their specific character forms no part of the present invention; the switches MIL, M2L and M3L, connected in parallel with each other, are connected, however, in circuit with a suitable current source and manual control switch therefor (not shown) and with the solenoid of contactor C so that when one or more of the switches are closed the solenoid may be energized from said current source and contactor C thus held closed to permit operation of the mill, but when all are open'this solenoid is deenergized and the mill motor driving circuit thereby interrupted to stop the mill. The functions of switch M4L will hereafter more fully appear.

The centrifugal control switch GSL to which reference has been made, is likewise actuated by shaft 25L through bevel gears 45L and through an additional cam on shaft 39L as will hereinafter more fully appear. This switch is identical with the corresponding switch GSR interconnected with the circuits for controlling the motors when the strip is being unwound from right hand reel MR and, as shown in Figs. 4-6, is mounted in a frame 50 providing suitable bearings for its driving shaft 25L or 253. of the left and right hand controls respectively. Each of the switches GSL, GSR comprises a substantially conical cup 5| insulated from but secured to a collar 52 carried by its supporting shaft 53 which effects its rotation through connection with gears 45. The interior of the cup forms a substantially frusto-conical recess communicating with a short cylindrical bore at its bottom, and contains a suitable quantity of an electrical conductive fluid F such as mercury. Electrical contact with the cup is made by means of a brush 54 engaging a collector ring 55 integral with the cup adjacent its midpoint, while the upper end of the cup is internally threaded for the reception of the externally threaded upper portion of a core 58. The latter comprises a generally conical body 51 having a central bore 58 communicating at its lower end through radial bores 59 with the outer cup chamber and with longitudinal groove 60, rectangular in cross section, which form, with the inner wall of the cup, a plurality of channels in which the fluid F can rise under the influence of the centrifugal force set up by rotation of the cup and the core. The upper end of the core is afforded lateral support through antifrictionbearings SI carried in the upper portion of the switch frame, and a cover plate 62 protects the bearings and forms with adjacent portions of the frame a chamber to retain a lubricant supply for the bearings BI. An insulating tube 63 extends from above this plate through its central bore and into the bore 58 of the core, and is secured in the core at its lower end by a pin 64. A plunger extends axially within the tube 63 and is supported by links 66 from a walking beam 61 pivoted on a standard 68 secured to a cross beam 69 of the main frame 50. A spring 10 is connected between the walking beam 81 and the cross beam 69 and urges the former to maintain the plunger in raised position through its connection adjacent the opposite end of the walking beam pivot from that of the plunger connection, this end of the walking beam being actuated through suitable linkage by a roller II which rides on a cam 12 carried by shaft 39L. Thus, when cam I2 is rotated by its actuating shaft, plunger 05 is raised and lowered in correspondence .with the contour of the cam, and the lower end of the plunger accordingly makes contact with'the mercury in the lower end of tube 63 or breaks such contact as the relation of its lower end to the. level of the mercury in the tube is varied. As noted, however, the channels formed by grooves communicate with the bore of tube 83 and,

since they extend angularly upwardly and outwardly, rotation of the cup sets up a centrifugal force which constrains the level of the mercury to rise in these channels and correspondingly to fall in tube 63, the extent of such raising and lowering being controlled by the speed of rotation of the cup, so that the making and breaking of contact between plunger 65' and the mer cury in the tube is thus controlled on the one hand by operation of cam 12 and on the other by the speed of rotation of the cup.

The cup SI of switch GSL and, hence, the mercury disposed therein, are in electrical connection through brush 54 with a lead III, while the plunger is in circuit with lead H3. The latter is connected to one pole of mercury switch MlL and the former to the other pole of said switch so that when switch M4L is closed, the governor switch GSL is shunted out and its operation throw switch SD which is connected in the generator field rheostat control circuit in such way that when its contacts SDI are closed through energization of the switch solenoid, the fields of the generator fleld rheostat motor are placed in circuit with switches J, K, actuated from the operator's desks LD, RD to permit .the operator to control the starting and acceleration of the mill and/or reel motors when rolling of a strip is being initiated as well as to control their speed during the major part of its passage between the reels during rolling. when the solenoid of switch SD is deenergized, however, the contacts SDI are opened, breaking circuits III, II. and III, II! to interrupt the manual control of the generator field rheostat motor and contacts SDI are closed, completing circuits 0-H! and illl2i| to energize this motor so as to cause it to reduce the generator field excitation and decelerate the mill.

While reference has herein been made to switches and other parts associated with left hand reel IOL and therefore designated by the suffix 14" appended to their distinguishing characters, it will be understood that like controlling mechanisms are associated with the right hand reel for a purpose which will hereinafter appear, and are so designated by the suflix "R".

Thus, right reel motor RRM drives aselsyn transmitter STIR corresponding to transmitter STIL, and receiver SRIR is connected with this transmitter through power leads I24, I", I" and the rotor connections III, III, I! so as to drive shaft HR. in correspondence with rotation of motor RRM A resetting motor R83 and a selsyn transmitter STIR are coupled to shaft 258, and transmitter STIR. is supplied with energizing current from transformer 20 through connection with leads I, I", its rotor being interconnected through leads I3l,' III, I32 with that of a selsyn receiver SRIR on left control desk LD, receiver SRIR driving a revolution counter IIL through a flexible coupling 30L. Switches MIR, M212, M311, MlR and GSR, corresponding to like switches in the left hand control, are actuated by corresponding cams, cam shafts and reducing gears driven from shaft "B. These switches are shunted out by suitable connections in the pass selector switch PS on the left control desk when their operation is not required, the same switch shunting out the corresponding ones in the left control when they similarly are not required.

Thus, when the strip is being rolled from left to right, pass selector switch PS interconnects leads Ill, I, shunting out switches GSR. and M43, and leads I36, I31 shunting out switches MIR, MIR, MIR, while for the reverse direction the connections are opened and leads I I3, I II and I35, I30 respectively interconnected, shunting out the corresponding switches GSL, MIL, and MIL, M2L, MIL.

Reference has been made to the raetting motors RSL, RSR which are provided for the purpose of rotating shafts 20L, 25R respectively to reset the control mechanism to proper starting position, i. e., when the counters iIR and IIL register 00000, whenever required, such resetting being usually necessary after the one strip has been rolled and before starting to roll another and also following the breakage of a single strip while it is being rolled or the occurrence of some other abnormal condition. The operation of the resetting motors RSL, BBB is controlled by switches (not shown) located in any convenient position, as for example, on the operating desks LD, RD, preferably so designed as to enable the motors to be operated at high, medium and extremely slow speeds to thereby permit the resetting of the mechanism to be accomplished rapidly and accurately. In addition to their function of controlling the resetting motors, the switches are also preferably arranged to interrupt the power circuits to the selsyn systems STI, SRI so that no motion will be communicated by the said systems to the reel motors during the resetting operation. Desirably, these switches are designed for manual actuation, and asthey may be of any type and construction suitable for the performance of their intended functions, detailed description or illustration thereof in the drawings is unnecessary.

Operation Preparatory to rolling a strip S, the controls associated with one of the reels, for example, reel IOL, are so adjusted, preferably by resetting motor RSL, that counter 3 IR reads zero, at which position, provided their operating cams have been properly set, switches MIL, MZL, M3L and MlL are open. By shunting out these switches through pass selector switch PS the circuit controlling contactor C maybe closed to start the mill to thereby initially wind the strip on reel IIIL. When all or substantially all the strip is wound thereon the mill is stopped, as by opening the circuit controlling contactor C by the manual switch in its power supply line and the free end of the strip then led through the rolls and secured to reel IOR. Counter'3IR now shows exactly the number of turns on reel I L, and as the end of the strip only is on reel IOR, the controls associated withthis reel are nowoperated toset counter 3IL to read zero, resetting motor RSR being conveniently utilized for this purpose. Switches MIR, MZR, M3R and M4R are now open and one or more of switches MIL, M2L, M3L are closed in accordance with the positions of their several cams. A circuit is thus established between leads I35, I36, and pass selector switch PS is next thrown to shunt out switches MIR, MZR, M3R and interconnect leads I36, I31, thus closing the circuitbetween leads I35, I31 and permitting the solenoid of contactor C in the generator output circuit to be energized trough its manual switch to start the mill motors and initiate the rolling operation. By means of switch J the operator may then control the operation of motor FM so as to speed up the mill motors'as desired to bring the mill to proper rolling speed in the usual way. The strip is thus progressively unwound from reel IIIL, rolled, and wound upon reel I 0R, one or more of switches MIL, MZL, M3L being kept closed throughout this period by the coordinated operation of their respective controlling cams which are actuated, as above noted, in synchronism with rotation of left reel IOL.

As the point at which deceleration is to commence approaches, that is, when all but the last few turns of the strip have been unwound from reel IIIL, the cam operating switch M4L opens it, so that it no longer shunts out governor switch GSL. When the cup of the latter is rotating at a relatively high rate of speed corresponding to that of unwinding reel IOL, the level of the mercury in tube 63 of this switch may be insuflicient to effect contact, with the plunger. The circuit through the solenoid of switch SD is therefore broken by the opening of switch MIL and the solenoid deenergized, thus causing contacts SDI to open, disconnecting the switches J and K, and contacts SDZ to close, thereby energizing the field rheostat motor through interconnection of leads II9, I 20 with leads I I5, I I8 respectively to cause a diminution in the generator voltage and reduce the mill motor speeds. Such reduction of the speed of the mill motors reduces the rate of rotation of unwinding reel IIIL and that of the cup of governor switch GSL. and thus results in a fall of the level of the mercury in the outer channels of the cup and a corresponding rise in its level in its central tube. When the mercury rises therein sufliciently to contact the end of the plunger, the circuit between leads III and H3 is again completed, reenergizing the solenoid of switch SD to disconnect leads H5, H8 from II9, I20 respectively and deenergize the field rheostat motor to prevent further diminution in the generator voltage. The mill now continues to 'operate at its reduced speed but during such operation cam 12 controlling the plunger in switch GSL is being rotated by its actuating mechanism hereinbefore described, gradually raising the plunger in the tube. The mercury having substantially ceased to rise therein, however, upon cessation of the voltage decrease and consequent interruption of the mill deceleration, the rising of the plunger under the influence of the cam breaks its contact with the mercury and again deenergizes the solenoid of switch SD, causing a further diminution in the generator voltage until the mercury again rises sufficiently. as a result of further diminished mill speed, to 'contact the plunger and again interrupt the deceleration.

Of course, if upon opening of switch M-IL by its cam the governor cup is rotating so slowly, due to a lesser rolling speed, that the plunger and mercury are in contact, the solenoid circuit is not immediately broken and the mill continues.

to operate at the same speed until a further amount of strip is withdrawn, corresponding to the plunger travel necessary to open the circuit by operation of the plunger cam but as soon as it does open, deceleration is initiated as above described and thereafter proceeds in like manner.

In practice, these coordinated operations irrespective of what the strip speed may be when they are initiated produce a gradual decrease in the generator voltage and hence in the strip speed throughout the deceleration period and until the end of the strip is very nearly reached, when the strip speed is relatively slow. As approximately the last turn of the strip on reel IOL is reached, the cams operating switches M3L and MZL, having already opened these switches, that operating switch MIL brings it into open position, to open the circuit between leads I35, I!" to deenergize the contactor C thus opening the main driving circuit to bring the mill motors to rest.

The strip having thus once been rolled in a single pass through rolls 2 from reel I 0L and now being wound upon reel IDR, the mill is operated in the opposite direction by suitable manipulation of reversing switch E, reel motor field rheostats and other mechanisms provided for the purpose. Thus, left reel motor LRM is positively driven in the opposite direction and mill motor A is reversed to draw the strip from the right reel and, after rolling, to rewind it upon the left one, right reel motor RRM meanwhile being so controlled for example by its field rheostat as to exercise the desired regenerative braking effect on right reel IllR. During this reversal the circuit between leads I35 and I3! is maintained by right hand switches MIR, M2R, M3R since the corresponding left hand control switches are shunted out by interconnection of the leads I35, H6 in pass selector switch PS. As the rolling proceeds, right hand governor switch GSR becomes effective, on the opening of right hand limit switch MdR toward the end of the pass, to effect deceleration of motors A and LRM through control oi the circuit through the solenoid of switch SD in the manner heretofore carried out by switch GSL, the latter being shunted out through the pass selector switch during the reverse operation of the mill. As the end of the strip on the now unwinding reel IDR is reached, the rate oi. rolling having been reduced to a minimum, limit switches M3R, MZR, having already been opened by their operating cams switch MIR is similarly opened and interrupts the circuit I35, I31 to open contactor C and deenergize all the mill motors, placing the entire system in condition for the next ensuing pass in the first direction upon proper manipulation of the pass selector switch PS.

The rolling of the strip is thus continued alternately in opposite directions until the desired reduction has been effected, the left hand control mechanism, parts of which are designated with the suffix L, being brought into play to de celerate and stop the mill when the last part of the strip is being unwound from the left hand reel I 0L and wound upon the right hand reel IUR, and the right hand control, corresponding parts of which are designated with the sufilx R, being employed to perform corresponding functions at the end of the passage of the strip in the opposite direction.

The rolls 2 are from time to time adjusted, of course, to a somewhat smaller pass and are driven by the motor A in opposite directions corresponding to the direction of the passage of the strip from reel iliL to reel IBR and back again. As each pass produces appreciable elongation of the strip, it is evident that each requires a greater number of turns of the winding reel to take up the entire strip than was required of the winding reel for the preceding pass. Furthermore, the thickness of the strip is reduced as its length is increased, and the practical maximum rolling speed thus correspondingly increases so that while during the first few passes, only a relatively slow movement of the strip from one reel to the other may be permitted, as the end of the operation is approached and during the last few passes, the speed of rolling may be as high as 1200 feet per minute or even higher. However, the automatic control of our invention, as herein described, and irrespective of the rolling speed, effects deceleration of the driving motors at a predetermined rate and automatically in accordance with the number of turns left on the unwinding reel so as to bring the motors to rest at the point where the maximum amount of strip is unwound from the unwinding reel without pulling the end loose therefrom.

The operation of a mill equipped with our control system and the relation between the rolling speed and the time required for complete deceleration therefrom may perhaps be better understood by reference to Fig. 8, in which points along the X-axis represent the amount of strip remaining on the unwinding reel while those on the Y-axis represent the strip speed which, as herein explained, is determined by the voltage output of generator G supplying driving current to the mill.

Thus, that portion of the curve v which substantially parallels the X-axis represents the maximum strip speed V at which the mill is capable of operating, and curves v and 12" respectively represent in their portion parallel to the same axis other arbitrarily selected speeds V' and V" at which the mill may operate in practice. In order to bring the mill from maximum speed V to rest at the proper point 0, i. e., when no or substantially no more strip can be removed from the unwinding reel without breaking the strip, it is necessary to initiate the deceleration of the mill when some predetermined amount of the strip remains on the unwinding reel, and the portion T0 of the curve 1: represents an assumed ideal deceleration curve for bringing the mill to rest at the point 0 after it has rolled the major part of the strip at maximum speed. It will now be assumed the mill is in operation under control of the system hereinabove described, and, for cleamess of explanation, at a speed V closely approaching the maximum speed V. When the point T is reached, 1. e., when a predetermined number of turns TO remains on the unwinding reel, cam I2 operates to open switch M4 01' the right or left control depending on the direction of rolling. As the speed V is slightly less than the speed V, it is not necessary to immediately initiate deceleration of the mill, however, so the governor GS maintains the circuit in solenoid SD for a short time after M4 opens and the mill continues to operate at the speed V until an additional amount of strip TU has been removed from the unwinding reel. During this period, the plunger of the governor is being raised by its cam but the speed of the governor corresponding to V' is such that the mercury is not maintained at a level low enough to break the governor circuit. However, as the amount of strip remaining on the reel becomes less than 0U, the plunger reaches a position sumciently elevated to break the governor circuit and switch SD is thereupon actuated to energize field rheostat motor FM to reduce the generator field excitation and in turn the strip speed. This motor is preferably arranged so that when operating at normal speed in the proper direction. it effects deceleration of the mill motors at a rate slightly greater than the "ideal" rate represented by the curve 0 so that the speed or the mill diminishes along a steeper curve p during further unwinding until it becomes less than the ideal or v-curve speed for that point in the strip, 1. e., until the mercury in the governor tube rises suiiiciently to contact the plunger to reenergize solenoid SD and arrest operation of the generator field rheostat motor. The mill then operates at constant speed q until the strip on the unwinding reel is reduced sufliciently to cause the governor switch to again operate the field rheostat motor as just described. The speed of the mill motors is thus in practice usually decreased by increments during the deceleration period and while in Fig. 8 we have shown it departing rather widely from the ideal" deceleration curve 11 for the sake of clearness of illustration, it will be understood that this departure may be greater or less depending on the desired ideal deceleration rate, the shape of the governor plunger actuating cam, the rate at which the generator field rheostat motor reduces the mill speed when it is in operation and other factors.

It will also be understood that when the mill is being operated at any other rolling speed, such as V", materially less than the maximum, it will be maintained at this Speed for a considerable period, TW, after switch M4 opens and thus until but OW turns remain on the unwinding reel, since obviously when the mill is operating at a slow speed, deceleration rates being equal, less time is necessary to bring it to rest than when it is operating at high speed. When all but OW turns have been removed; however, deceleration of the mill is initiated as hereinabove described to ultimately bring the mill to rest at point 0.

Of course, the various mechanisms may be so arranged that once deceleration is initiated the generator field rheostat motor is kept in constant operation throughout the deceleration period, and the deceleration curve 1) is exactly adhered to by the strip speed, but we prefer to operate the system to maintain a controlled deceleration in relation to the strip speed as above described.

While we have herein shown and described one embodiment of our invention with considerable particularity, and especially as it may be employed for controlling a typical strip mill of a specific character, it is to be understood that we do not desire or intend that our invention shall thereby in any way be limited or restricted in its employment as a control system for other mills or for mechanisms of different character, nor do we confine ourselves to the said specific embodiment of our invention as the latter may readily be modified to suit varying conditions and to' perform various functions other than those herein particularly mentioned; moreover, changes and modifications in the form, construction and arrangement of the several mechanisms employed, the parts thereof and the manner of their interconnection will readily occur to those skilled in the art and may be made if desired without departing from the spirit and scope of the invention as defined in the appended claims.

Having thus described our invention, we claim and desire to protect by Letters Patent of the United States:

1. The combination with a current source, control means therefor operable to progressively diminish the current delivered therefrom and an electric motor energized by said delivered current, of means actuated by the motor operative to successively energize and deenergize the control means to thereby efiect progressive diminution of the motor torque in predetermined timed relation with the movement of the motor and means actuated from the motor actuated means for interrupting said current at a predetermined interval after the control means are first brought into operation.

2. The combination with a current source and an electric motor actuated thereby, of a centrifugally responsive switch'driven by the motor and motor current control means adapted to be energized thereby operative to control the motorto effect progressive diminution of its torque in predetermined timed relationwith the movement of the motor and another switch having a common drive with the first switch operative to deenergize source, and means interconnecting the cup and the plunger in circuit with said control means to effect progressive deceleration of the motor.

4. In combination with a pair of electric motors, means for driving each of said motors electrically, means interconnecting the motors for mechanically driving each from the other while either is being driven electrically, means respectively actuated by each motor operative while said motor is being mechanically driven to control the voltage supplied to the other motor to effect progressive deceleration thereof in predetermined relation to the rotation of the motor being driven mechanically therefrom.

5. In combination with a pair of electric motors, a source of current supply therefor, means for reducing the current so as to decelerate the motors and means mechanically interconnecting the motors, a control system operative to actuate said current reducing means in predetermined timed relation with the rotation of one of the motors comprising a switch interconnected with the current reducing means and means driven by saidmotor for actuating said switch.

6. In combination with a pair of electric motors, a source of current supply therefor, means for reducing the current so as to decelerate the motors and means mechanically interconnecting the motors to drive either from the other, a control system adapted to automatically actuate said current reducing means comprising a switch, means for actuating said switch in correspondence with the rotation of the driven motor, and another switch in circuit across the contacts of said first mentioned switch operative to shunt out the first mentioned switch during a predetermined period of operation of thedriven motor.

'7. In combination with a pair of electric motors, a source of current supply therefor, current control means for reducing and finally shutting off the current so as to decelerate the motors and finally to bring them to rest, and means selectively actuated by either motor to drive the other motor therefrom, a control system comprising switch means operative to actuate the current control means to progressively decelerate the driving motor during a predetermined number of revolutions of the driven motor, and other switch means also interconnected therewith operativc to actuate the current control means to shut off the current during the next ensuing revolution of the driven motor.

8. In combination with a pair of electric motors, a source of current supply therefor, current control means for reducing and finally shutting off the current so as to decelerate the motors and finally to bring them to rest, and means selectively actuated by either motor to drive the other motor therefrom, a control system comprising a switch in circuit with the current con trol means actuated in accordance with the number of revolutions made by the driven motor operative at a predetermined point in the operation thereof to interrupt the switch circuit, centrifugal governing means thereafter operative to successively energize and deenergize the current control means to effect progressive deceleration of the motors through an ensuing predetermined number of revolutions of the driven motor, other switch means for interrupting the flow of current to the motors after said revolutions have been accomplished, and means actuated in accordance with the rotation 01 the .driven motor for actuating all of said switch means.

9. The combination with a pair of winding reels and respective driving motors therefor adapted to alternately unwind a strip from one reel and wind it on the other, of control means for the motors automatically operative to decelerate the then winding reel-in predetermined relation to the number of revolutions thereafter to be made by the other reel comprising switch means actuated in accordance with the rotation of said other reel operative to progressively reduce the flow of current through the winding reel motor.

10. The combination with a pair of winding reels and respective driving motors therefor adapted to alternately unwind a strip from one reel and wind it on the other, of control means for the motors automatically operative to de celerate the motor of the then winding reel in predetermined relation to the number of revolutions thereafter to be made by the other motor comprising switch means actuated in accordance with the rotation of said motor operative to reduce the flow of current through the winding reel motor during the subsequent revolutions of the other motor, and other switch means for interrupting said current at the conclusion of said subsequent revolutions.

11. The combination with a pair of reels and respective driving motors therefor operable to alternately unwind a strip from one reel and wind it on the other, of control means for the motors operative in accordance with the number of revolutions made by the unwinding reel to reduce the current flowing through the winding reel motor to effect deceleration thereof during a predetermined number of the revolutions of the unwinding reel, said means comprising a shaft, means for rotating the shaft in correspondence with the rotation of the unwinding reel, switch means actuated by said shaft operative to progressively reduce the current to the winding reel motor upon completion of a predetermined number of revolutions of the shaft prior to attainment of its limit of rotation as determined by said strip, and governing means for thereafter controlling the rate of deceleration of said motor during the period of deceleration.

12. The combination with a pair of reels and respective driving motors therefor operable to alternately unwind a strip from one reel and wind it on the other, of control means for the motors operative in accordance'with the number of revolutions made by the unwinding reel to reduce the current flowing through the winding reel motor to effect deceleration thereof during a predetermined number of revolutions of the unwinding reel, said means comprising a shaft, means for rotating the shaft in correspondence with the rotation of the unwinding reel, switch means actuated by said shaft operative to progressively reduce the current to the winding reel motor upon'completion of a predetermined number of revolutions of the shaft prior to attainment of its limit of rotation as determined by said strip, governing means for thereafter controlling the rate of deceleration of said motor during the period of decelerationjand other switch means opdriving motor for each reel whereby a strip may be unwound from one reel and wound on the other reel, a control system operative to automatically reduce the current flowing to the motor of the windingreel after the unwinding reel has made a predetermined number of turns so as to decelerate said motor during an ensuing predetermined number of such turns, and to then shut off the current to said motor, comprising a cam actuated switch, means for actuating said switch in correspondence with the turns of the unwinding reel to reduce said current after a predetermined number of said turns, governing means actuated by said switch actuating means for controlling the rate of deceleration of the winding reel motor resulting from the reduction of its current during a further predetermined number of turns of the unwinding reel, and other switch means also actuated from said actuating means for then shutting off the current to said motor.

14. In combination with a pair of reels, 9. driving motor for each reel and a source of motor driving current whereby a strip may be unwound from one reel, and wound on the other reel, a control system operative to automatically reduce the current flowing to the motor of the winding reel after the unwinding reel has made a predetermined number of turns so as to decelerate said motors during an ensuing predetermined number of such turns, and to then shut off the current to said motors, comprising electrical means operative to reduce the current flowing to said motors, centrifugally responsive switch means operative to regulate said electrical means to control the rate of deceleration of the motors, a cam' actuated switch operative to render the centrifugally responsive means effective only during a predetermined number of turns of the unwinding reel, other switch means for then interrupting said current to bring the motors to rest, and means for actuating each of said switch means in accordance with the rotation of the unwinding reel motor. c

15. The combination with a strip mill comprising a pair of reels and a driving motor for each reel whereby a strip wound on one reel may be unwound therefrom and wound on the other reel, of a control system for said motors comprising revolution counters for respectively recording positively and negatively the revolutions of each reel, means for actuating each counter in accordance with the movement in either direction of its respective reel, switch means including a centrifugally responsive fluid governor interconnected with the means actuating the counter recording the negative revolutions of the unwinding reel operative on the' attainment of a predetermined number of said revolutions to reduce the. current flowing to the winding reel motor and thereafter to regulate the average rate of motor deceleration induced by such reduction during an ensuing predetermined number of negative revolutions of the unwinding reel, and other switch means also actuated from said counter actuating means for then interrupting said current to bring both said motors to rest.

16. In an electrical control system, a plurality of cam actuated switches interconnected in parallel, a cam for actuating each switch, a shaft supporting each cam and reducing gears interposed between each shaft and an adjacent one operative to effect differential rotation of the several shafts in predetermined relation with the operation of the controlled mechanism to thereby simultaneously actuate all of said switches at a predetermined point in said operation.

1'7. A centrifugally responsive control switch comprising a support, a cup rotatable in said support, means for rotating the cup, electrically conductive fluid disposed in the cup, a plunger carried by the support having an end extending axially into the cup, and adapted to effect contact with said fluid when the cup is rotating and means for effecting movement of the plunger relatively to the fluid in timed relation with the rotation of the cup.

18. A centrifugally responsive control switch comprising a support, a cup rotatable in said support, means for rotating the cup, electrically conductive fluid disposed in the cup, a plunger carried by the support having an end extending axially into the cup, and adapted to effect contact with said fluid when the cup is rotating at a speed not greater than a predetermined speed, and means actuated from the cup rotating means for moving said plunger axially in the cup to thereby selectively make and break contact thereof with said fluid independently of the speed of rotation of the cup.

19. In an electrical switch, a rotatable cup having an inverted frusto-conical chamber, a frustoconical core disposed in said chamber having longitudinal grooves forming channels with the walls thereof, an axial bore, and passages interconnecting said bore and said channels,'electrically conductive fluid in said bore, channels and passages, a plunger extending longitudinally in said bore operable to make and break contact with said fluid, and means operative to efiect vertical movement of the plunger in predetermined timed relation with the rotation of the cup.

20. In combination with an electric motor, means for supplying driving current thereto and means operable to diminish said driving current, means actuated from the motor operable to actuate said current diminishing means intermittently in predetermined timed relation with the operation of the motor to progressively reduce the motor speed, and other means actuated from said motor actuated means operative to interrupt the driving current when the motor reaches a predetermined reduced speed to thereby bring the motor gradually to rest.

21. In combination with an electric motor. means for supplying driving current thereto and means operable to diminish said driving current, a control system operable to actuate said current diminishing means comprising a control circuit, means for successively opening and closing said circuit in predetermined timed relation with the operation of the motor to thereby progressively diminish the driving current to decelerate the motor, and a second circuit including means for interrupting the driving current, and means for controlling the second circuit to interrupt the driving current in predetermined timed relation with the operation of the first circuit.

22. In a motor control system, a motor driving current control circuit, means actuated from the motor in timed relation with its rotation operable to successively energize and deenergize said circuit in accordance with the motor speed thereby to effect progressive subsidence of the motor driving current and means actuated by said motor actuated means for interrupting said current when it reaches a predetermined diminished value.

23. In a motor control system, a motor driving current control circuit, a switch for opening and closing said circuit, means operable to actuate said switch, means driven from the motor in timed relation with its rotation operable to successively energize and deenergize said switch actuating means in accordance with the speed of the motor to thereby cause progressive subsidence of the motor driving current and another switch actuated by said motor driven means for finally interrupting said current to stop the motor.

GILBERT EDWARD ADAMS.

EDWARD CRU'ICHFIELD MARSHALL. 

